This proposal concerns the further structural and functional characterization of two lipopolysaccharide (LPS)-binding antimicrobial protein from PMNs, the bactericidal/permeability increasing protein (BPI) and the 15 kDa protein isoforms (p15s), and the study of the role and regulation of BPI and p15 function in inflammatory exudates. These proteins have been isolated and cloned in this laboratory and implicated as important mediators of host antimicrobial activity against Gram-negative bacteria (GNB) and as negative regulators of host responses to endotoxin (LPS). The specific aims are (1) to further define the molecular determinants of BPI function, (2) to further characterize the structural and functional properties of the p15s and to identify p15 homologues in other species, and (3) to determine the role and regulation of BPI and p15 function in inflammatory exudates and to characterize BPI-independent antimicrobial activity in inflammatory fluids, Insights gained from this work will likely provide a better understanding of endogenous mechanisms that determine host responses to endotoxin and defense against invading GNB and help in designing specific therapeutic agents for the treatment of invasive GNB infections and endotoxeimia when endogenous defenses and conventional antibiotics are inadequate.